This invention relates to liquid ring pumps, and more particularly to check valve structures for the auxiliary discharge ports that are sometimes provided in liquid ring pumps.
As shown, for example, in Siemen U.S. Pat. No. 1,180,613, it is known to provide liquid ring pumps with multiple, circumferentially spaced gas discharge ports, the discharge port which is most distant from the gas inlet port in the direction of rotor rotation being the main discharge port, and the other discharge ports being auxiliary discharge ports. It is also known to associate check valves with the auxiliary discharge port or ports so that they open automatically to release gas from the pump when required. When the pump is not compressing gas to the final discharge pressure adjacent to an auxiliary port, the check valve associated with that auxiliary port closes automatically to prevent gas discharged by the pump from re-entering the pump via the closed auxiliary discharge port. Auxiliary discharge ports with check valves may be used for such purposes as preventing unduly high gas pressure in the pump during abnormal operating conditions (e.g., when the pump is first started) and/or extending the operating range of the pump.
In most prior liquid ring pumps with auxiliary discharge ports and check valves, the check valves are located right at the auxiliary discharge ports. Thus in Schroder U.S. Pat. No. 3,366,314, German Offenlegungsschrift 2,704,863, British patent application 2,064,002A, and Japanese patent application 55-5428, for example, the check valve balls or flappers are located right on the side of the port plate or port member which is immediately outside the working portion of the pump. On the other hand, in some "internally ported" liquid ring pumps the check valves are located in the interior of the frustoconical or cylindrical port member that extends into a complementary recess in an axial end of the pump rotor (see, for example, Dardelet U.S. Pat. No. 2,344,396, Kollsman U.S. Pat. No. 2,453,373, British patent 11,378 of 1905, and Japanese patent application 55-5427).
The above-described conventional check valve locations may be undesirable for any of several reasons. The working spaces of the pump vented by the auxiliary discharge ports typically have complicated shapes such as trapezoids or generally trapezoidal shapes with one or more curved sides. Even in the case of internally ported pumps with check valves on the axial end of the port member rather than inside the port member, the auxiliary discharge port passageways typically have trapezoidal cross sections in order to help keep the diameter or circumference of the pump as small as possible. It is difficult to provide check valves for such trapezoidal shapes without somewhat restricting the flow of gas exiting from the pump via those valves even when the valves are open. For example, ball check valves generally require a circular seat, but there may not be room on the axial end face of the port member to provide a circular seat having the same gas flow area as the trapezoidal port to be served by that seat and its associated ball. Indeed, because of the presence of the ball adjacent the seat even when the valve is open, there may be undesirable pressure drop across the check valve unless the flow area through the seat can be made greater than the trapezoidal area leading to the seat. Flapper valves can have a trapezoidal shape, but they require relatively broad seats in order to seal properly and avoid being pulled through their seats by substantial backpressure. A substantial area must also be devoted to mounting the flapper member. Thus again there may not be room at the axial end of the port member for an adequate flapper valve seat and mounting without constricting the associated trapezoidal auxiliary gas discharge port.
Among the disadvantages of locating the check valves inside the port member of an internally ported pump (as in the above-mentioned Dardelet and Kollsman patents, for example) are that doing so makes the check valves relatively inaccessible for maintenance and also tends to be contrary to the objective of keeping the diameter or circumference of the pump as small as possible.
Bissell et al. U.S. Pat. No. 4,498,844 shows a conically ported pump with a vent-recirculation port 76 (FIG. 10) that leads to a conduit 84 in the head member outside the port member. Conduit 84 in turn leads to a liquid sump 100 (FIG. 4) in the bottom of the head member. A further auxiliary vent port 72 may communicate with conduit 84 via check valve 92. Because conduit 84 enters sump 100 below the normal level of liquid in the sump, gas cannot exit from either port 72 or 76 without experiencing some pressure drop associated with passing through the sump liquid.
Mugele U.S. Pat. No. 3,721,508 purports to show pumps with auxiliary discharge ports 13 having check valves 11 at locations remote from the port member. However, the Mugele patent appears to be largely schematic and does not show any attempt to optimize the depicted pumps with regard to such features as circumferential size. Moreover, although check valves 11 have been removed to locations that are remote from the port member, the check valve seats do not appear to be any larger than the ports 13 or conduits 9 leading to them. Check valves 11 can therefore be expected to produce undesirable pressure drops in the gas exiting from the pumps via those valves. This is especially undesirable if the auxiliary ports are provided to extend the normal operating range of the pump rather than only to provide pressure relief during relatively brief periods of abnormal operation.
In view of the foregoing, it is an object of this invention to provide improved check valve structures for liquid ring pumps.
It is a more particular object of this invention to provide check valve structures for liquid ring pumps which include relatively large check valves that do not impede the flow of gas exiting from the pump via the check valve and which check valves can be located for easy maintenance.